Gallery – Koekedouw Dam Ceres

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Explore our galleries to truly experience the beauty of Koekedouw Dam.

The Old Dam (1953-1996)Preparatory Works Dam Foundation & Drainage Asphalt Concrete Base Rock Fill Instrumentation Outlet Works & Overflow Channel News Articles The New Dam

The Old Dam (1953-1996)

The old familiar Ceres Dam with its unique tranquility was located west of the town in the Koekedouw River with its natural fynbos slopes. The new dam is 3 times higher, holds 42 times more water, and is built in the same place.

The last memories of the noise and surges of the siphon overflow system that were responsible for the unpredictable flood waves in the lower river. Such waves often built up in less than a minute and cost adventurers their lives in some cases.

The southern view of the former 20-meter-high old concrete arch dam shows the walkway on the left with the siphon overflow in the middle. It is already empty and ready to be demolished.

December 1996 – The end of an era approaches and the first blast echoes with the demolition of the old familiar Ceres Dam. In the background is the temporary cofferdam, which would take over the water supply function for the bridging period of two years.

Preparatory Works

The central section of the arch structure had to be removed to eliminate its influence on the new type of gravity structure.

The temporary cofferdam, which now lies intact at the bottom of the larger dam, was responsible for supplying water to the Ceres Municipality and the Koekedouw Irrigation Board during the bridging period. It had a similar storage capacity to that of the old dam.

The steep access road along the southern slopes provides access to the dam’s walkway ruins. Special design techniques, such as steel-reinforced rock fill, were used to support the road at the top hairpin turn.

The middle panel of the deck, from the bridge at the distribution point in the mountain, is being cast. A total of four similar bridges have replaced the previous low-water bridges to establish a suitable access road to the new dam.

This is what the completed road looks like at the bridge below the distribution point. On the right is the flooded low-water bridge as it was for the old road.

The 5 mega-liter reservoir on Groenplaatjies, which was necessary during the bridging period to provide uninterrupted water to Ceres Municipality. To save costs, the roof was cast on the floor in the dam. Afterward, water was slowly let in to float it to the predetermined position on the pillars where it was to come to rest.

Dam Foundation & Drainage

A temporary road made of synthetic fiber material with a layer of gravel on top had to be built over the silty sand first to gain access, after which it was excavated along with the silty sand and dumped elsewhere.

Incidents like this were the cause of many frustrations during the removal of the soft silty sand from the old dam basin before construction of the embankment could begin.

Due to the fractured nature of the rock in the embankment foundation, a specialized drainage system was installed under the embankment to collect seepage water from specific areas and divert it to where it can be measured.

Asphalt Concrete Base

After the foundation for the embankment core was excavated down to solid rock, a reinforced concrete strip was placed over the entire length of the embankment, serving as the base for the asphalt core.

Holes, more than 40 meters deep, were drilled along the middle of the embankment core, after which cement was pumped under high pressure into them to seal all cracks in the fractured underground rock formation. In the background are the remnants of the old concrete dam.

The concrete surface was treated with acid to ensure good adhesion between the asphalt core and the concrete base.

A tough mixture of sand and bitumen was spread on the concrete foundation under the new embankment. It binds the asphalt core to the concrete base. In the foreground is a well and pumping system to collect the underground water and pump it out, thus ensuring suitable working conditions.

Hot asphalt concrete was transported from the mixing plant with a modified loader and tipped, after which, in this case, it was manually spread in formwork and then compacted. Both the upstream and downstream support fill materials were raised concurrently.

The placement of the hot asphalt concrete along with the two support layers was done by the specially modified paving machine. It was then compacted. This paving machine was specially imported from Norway for the contract. The layer thickness at which the core was placed was controlled by laser.

Two special rollers compacted the support layers on either side of the hot-laid asphalt concrete, after which the asphalt itself was compacted separately

Rock Fill

A flood wall to contain the floods and temporarily divert the water through the tunnel had to be built to ensure that work in the riverbed could proceed unhindered. This flood wall formed part of the larger embankment. The temporary steel water supply pipe, in the foreground, was also later rerouted through the tunnel.

General progress shows the completed flood wall with the remnants of the old concrete in the foreground. The temporary cofferdam responsible for water supply during the bridging period is visible in the background.

The quarry on the western bank just upstream of the embankment is approximately 45 meters deep. Rock products such as crushed stone and gravel for the asphalt core, various sizes of crushed stone and gravel for drainage purposes within the embankment, as well as crushed stone and sand for the concrete works, were produced using a rock crusher plant. Rock fill material for embankment construction purposes was blasted directly into the quarry using sophisticated explosive techniques according to regulations.

The southern view over the construction works shows: on the left – the white asphalt concrete mixing plant; central – the yellow conventional concrete mixing plant; in the foreground – the arch-shaped concrete spillway; on the right in the background – the 98% completed dam wall with the visible 0.5 meter wide central asphalt concrete core; on the left in the background – the temporary cofferdam.

General embankment construction activities: bottom left and top right – excavated material is being transported and tipped from the quarry; left – a roller is compacting the previous layer of rock fill; the black strip in the middle is the asphalt core with specialized support layers on either side; right – tipped rock fill material is being leveled by a push scraper to be compacted as a newer layer, across from it, the reinforced concrete foundation on which the asphalt core stands is visible.

Excavated rock material had to be temporarily stored upstream of the embankment due to the delayed progress with the embankment construction process caused by issues with compacting the underground foundation. On the right in the background is the rock crusher used to produce the special rock products.

The completed rock-fill dam is 62 meters high with a rock-fill volume of 640,000 cubic meters. The crest length is 280 meters long, and the base width along the old river line is 190 meters. The dam’s storage capacity is 17 million cubic meters.

Instrumentation

Six electronic sensors are installed under the embankment in the rock formation. They measure water pressure and temperature, which are important for analyzing the underground and seepage water throughout the embankment. This information is then regularly relayed via radio to the control center.

Two inclinometer and settlement instruments are also installed in the embankment. Each consists of a series of pipe segments extending from the foundation to the crest. Measurements are taken by allowing specialized instruments to descend inside them. Their function is to record any degree of three-dimensional movement of the embankment for analysis.

Outlet Works & Overflow Channel

The 4-meter diameter tunnel, which houses the main outlet pipes, is lined with a reinforced concrete floor. The floor section has already been completed, and construction workers are preparing the roof section.

The bottom inlet of the tunnel is visible at the southern corner of the quarry. It is approximately 40 meters below the full water level. Its function is to serve as a flushing outlet as well as for draining the dam in case of emergency.

In the background is the tunnel outlet. In the foreground, centrally located, are the steps of the spillway channel where it connects to the stilling basin in the riverbed. The temporary 600mm steel water supply pipe, which connects the existing pipe system through the tunnel to the temporary cofferdam, had to be maintained and operational during construction.

The formwork for the tunnel and tower connection section is ready for the concrete pouring.

The outlet control tower is located inside the dam. Construction workers are busy with the upper ring beam, which serves as support for the trash racks. The concrete roof of the control tower is still pending.

The foundation of the ogee-shaped spillway crest in the trough has been completed. The spillway trough serves as a collection channel for turbulent overflow water before it is directed down through the stepped spillway channel along the right bank back into the river course.

The 15-meter wide stepped concrete spillway channel on the right bank serves as an energy dissipator for overflow water. The openings beneath each step serve a dual purpose. They function as both a drainage and an aeration system. Negative pressure during flooding causes air to be sucked through the inlets at the top of the channel walls, thereby breaking up the water into a foaming mass.

The stilling basin in the riverbed at the bottom of the spillway channel serves as an energy dissipator to calm floodwater before it is returned to the river course.

Floodwater flows into the tunnel opening on the quarry side. The temporary 1-meter diameter pipe could only carry the normal river flow, allowing work to continue uninterrupted inside the tunnel.

Floodwater enters the tunnel opening on the side of the village near the remnants of the old dam. The purpose of the steel pipe was to convey river flow during normal conditions, allowing work inside the tunnel to proceed uninterrupted.